import 'dart:math';

class GpsCorrectHelper {
  static double pi = 3.14159265358979324;

  static double a = 6378245.0;

  static double ee = 0.00669342162296594323;

  static void transform(double wgLat, double wgLon, List<double> latlng) {
    if (_outOfChina(wgLat, wgLon)) {
      latlng[0] = wgLat;
      latlng[1] = wgLon;
      return;
    }
    double dLat = _transformLat(wgLon - 105.0, wgLat - 35.0);
    double dLon = _transformLon(wgLon - 105.0, wgLat - 35.0);
    double radLat = wgLat / 180.0 * pi;
    double magic = sin(radLat);
    magic = 1 - ee * magic * magic;
    double sqrtMagic = sqrt(magic);
    dLat = (dLat * 180.0) / ((a * (1 - ee)) / (magic * sqrtMagic) * pi);
    dLon = (dLon * 180.0) / (a / sqrtMagic * cos(radLat) * pi);
    latlng[0] = wgLat + dLat;
    latlng[1] = wgLon + dLon;
  }

  static bool _outOfChina(double lat, double lon) {
    if (lon < 72.004 || lon > 137.8347) {
      return true;
    }
    if (lat < 0.8293 || lat > 55.8271) {
      return true;
    }
    return false;
  }

  static double _transformLat(double x, double y) {
    double ret = -100.0 + 2.0 * x + 3.0 * y + 0.2 * y * y + 0.1 * x * y + 0.2 * sqrt(x.abs());
    ret += (20.0 * sin(6.0 * x * pi) + 20.0 * sin(2.0 * x * pi)) * 2.0 / 3.0;
    ret += (20.0 * sin(y * pi) + 40.0 * sin(y / 3.0 * pi)) * 2.0 / 3.0;
    ret += (160.0 * sin(y / 12.0 * pi) + 320 * sin(y * pi / 30.0)) * 2.0 / 3.0;
    return ret;
  }

  static double _transformLon(double x, double y) {
    double ret = 300.0 + x + 2.0 * y + 0.1 * x * x + 0.1 * x * y + 0.1 * sqrt(x.abs());
    ret += (20.0 * sin(6.0 * x * pi) + 20.0 * sin(2.0 * x * pi)) * 2.0 / 3.0;
    ret += (20.0 * sin(x * pi) + 40.0 * sin(x / 3.0 * pi)) * 2.0 / 3.0;
    ret += (150.0 * sin(x / 12.0 * pi) + 300.0 * sin(x / 30.0 * pi)) * 2.0 / 3.0;
    return ret;
  }
}
